The number of concurrent sessions or threads is unlimited, but all proxies are subject to Fair Use. You can use a single ISP or Datacenter proxy on multiple devices as long as they’re on the same network (with the same IP address). If you need to use a single IP across multiple devices (and networks) simultaneously, you can get a "Multi-device access" add-on when creating an order.
Currently, multi-device access is available in the following configurations: 3, 5, or 10 additional IPs per proxy. Each additional IP is priced at 50% of your order fee.
The Residential plan does not have this limitation - you can use it from an unlimited number of devices or IP addresses simultaneously.